Current technologies used for detection of explosive traces are based on direct air sampling of explosive vapor surrounding explosive contraband or are based on a particulate sampling technique. The direct air sampling technique is effective only for sufficiently volatile explosive components, while the explosive components mostly used for creation of so-called plastic explosives feature very low or zero volatility at ambient temperature.
There is a world-wide demand for reliable contact-less explosive detection technologies, being capable to sample and detect all kinds of explosive compounds, mainly widely used non-volatile or home-made explosive agents.
Most of the current detection technologies use an IMS (Ion Mobility Spectrometry) detection principle, or other technologies focused for direct identification of the sample. Unfortunately, those detection principles are very sensitive to cross-talk by various disturbing chemicals and saturation due to very limited dynamic range. Both above mentioned limitations create potentially a high false alarm rate and cause moreover a number of serious problems with after-exposure cleaning of the system.
The current portable system works mostly in the cycle “sampling—pre-concentration—analysis”. This operation cycle requires an operator to sample just from one spot, in the good belief this spot contains the found traces. There is no indication about the properly selected spot during the sampling interval, so it frequently happens to sample from the improper spot or location, while losing valid operational time.
Most of the current systems utilizing various detection technologies, namely IMS, are quite complicated, climatic condition-sensitive instruments, and are not very suitable for heavy-duty field and/or military application. Also, they require an advanced level of operator's qualification and demanding training of the operator.
Most of today's operators need to scan the controlled subjects (parcels, baggage, people) only in vapor mode, which under standard sampling conditions is typically not successful, namely in the case of plastic explosives (and all other non-volatile explosives). Such substances create no vapors at normal ambient temperature and hence no vapor traces can be sampled/detected in standard vapor mode.
Systems and methods for reliable detection of various explosives are urgently needed and are now at the forefront of many research efforts. The wanted detection system should be reliable, sensitive, of a small size for handheld use, operating preferably only in vapor mode, resistant against cross-talking chemicals to avoid false alarms and simple for operation, so as not to require extensive training or special education of an operator. Under the standard environmental conditions, the detection of explosives is a complicated and complex task, especially considering the detection of all variants of non-volatile types of explosives and disturbing factors of the variety of environmental condition (humidity, dust, temperature). Moreover, interference from various chemicals, human sweat, various solvents etc. lead to false alarms, which are obviously difficult to distinguish from actual positive detection.
The wide variety of techniques used to sample explosives include the manual swiping of the scanned subject in a so-called particulate mode or the sampling of air surrounding the scanned subject at ambient temperature and consequent pre-concentration in a good belief to collect most of the traces in the vicinity of the scanned subject. The manual swiping is not very popular or sometimes difficult to apply and the air sampling requires huge amount of air to be sampled and pre-concentrated to collect enough volume of traces to satisfy the system detection limit.
The variety of techniques used to detect/analyze explosives, based on ion mobility spectrometry, infrared spectroscopy, micro-wave spectroscopy, Raman or fluorescence spectrometry, bring good detection results. However all those principles feature low dynamic range and are sensitive to cross-talk caused by interfering chemicals or overload and suffer from difficult cleaning if exposed by huge sampled concentration. Portable detection systems built on above principles are usually complicated, big, heavy and not operationally robust enough to work reliably in the demanding field conditions, which are characterized by changing humidity, temperature, dust and rough handling by the operator. A high level of operator training and adequate operator education is obviously necessary for successful detection using above technologies, which limits the range of people usable to execute the detection operation.